Web feed mechanism

Abstract

 Herein disclosed is a web feed mechanism for stepwise or continuously feeding a web (1) such as a printing medium of a printer of the like from a roll of web. In the web feed mechanism, a slackness, if any, can be absorbed by applying a drag to the outermost portion of the web roll (1) and by causing a biased sliding member (9, 12) to slide in the tangential directions (C, D) of the web roll both forward (C), in which the web is to be let off from the web roll, and backward (D), in which the web is to be taken up onto the web roll.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates to a feed mechanism for feeding a web such as a printing medium of a printer or the like and, more particularly, to a web feed mechanism which is effective for a stepwise feeding a web haivng a small thickness.

Description of the Prior Art

[0002] The feed mechanism of the above-specified kind according to the prior art is equipped with nothing but a dragging mechanism. In case the feed mechanism is operated for the stepwise feed, a web being fed may frequently overrun to become slack on its running path so that the tension applied thereto on the path cannot be constant to invite a defect that the web makes noises and/or undergoes in an undulating manner.

SUMMARY OF THE INVENTION

[0003] The present invention has been conceived in view of the above-specified defect and has an object to provide a web feed mechanism which can hold a web on a running path under a constant tension so that it can be freed from noises.

[0004] According to a feature of the present invention, there is provided a web feed mechanism for feeding a web under a constant tension from a roll of web, comprising: a carrier made movable toward and away from the center of the web roll and biased toward the same center; a slide carried on said carrier in both manners to contact with the outermost web portion of said web roll and to slide in the tangential directions of said web roll both forward, in which said web is to be let off from said web roll, and backward, in which said web is to be taken up onto said web roll, for applying a drag to said outermost web portion; and bias means for biasing said slide in said backward direction to hold the let-off portion of said web under such a predetermined tension during the web letting- off operation as is caused by the balance between said drag and a pullying force of the let-off portion of said'web, whereby the let-off portion of said web can be prevented from noises and/or undulating runs which can might otherwise be caused by the fluctuations of the tension applied thereto.

[0005] According to another feature of the present invention, there is provided a web feed mechanism for stepwise feeding a web, while tensing the same, from a roll of web, comprising: a carrier made movable torward and away from the center of the web roll and biased toward the same center; a slide carried on said carrier in both manners to contact with the outermost web portion of said web roll and to slide in the tangential directions of said web roll both forward, in which said web is to be let off from said web roll, and backward, in which said web is to be taken up onto said web roll, for applying a drag to said outermost web portion; and bias means for biasing said slide in said backward direction, said bias means being adapted both to have its biasing force strengthened by a pulling force of the let-off portion of said web through a frictional force between said slide and said outermost web portion, while tensing the let-off portion of said web, until said slide is brought in said forward direction into a first position during one feed stroke of said web against the biasing force of said bias means being strengthened and to cause said slide to frictionally slide in said backward direction on the outermost web portion of said web roll into a second position by the strengthened biasing force which has overcome said pulling force after said one feed stroke, while spinning back said web roll, thereby to absorb a slackness, if any due to the overrun of the let-off portion of said web, through the backward sliding movement of said slide.

[0006] In short, according to the present invention, there is provided a web feed mechanism which is enabled to absorb the slackness of the web on the running path by applying a drag to the outermost portion of the web roll and by causing the slide to slide in the tangential directions of the web roll both forward, in which the web is to be let off from the web roll, and backward, in which the web is to be taken up onto the web roll.

BRIEF DESCRIPTION OF THE DRAWING

[0007] Other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawing, in which:

Fig. 1 is a schematic view showing a web feed mechanism according to one embodiment of the present invention; and

Fig. 2 is an enlarged schematic view for illustrating the operating principle of the web feed mechanism by showing an essential portion of Fig. 1 in an enlarged scale.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0008] The present invention will be described in the following in connection with the embodiment thereof with reference to the accompanying drawing in case it is applied to a feed mechanism for feeding the heat transfer carbon paper or ribbon of a heat transfer type thermal printer.

[0009] As shown in Fig. 1, the heat transfer carbon paper or web 1 is held in the form of a roll on a core 2 acting as a holding member. The heat transfer carbon paper 1 is let off is fed to a clearance between a thermal head 3 and a platen roller 4 so that it can be used to print a continuous web of labels L, until it is fed out by the coactions of the platen roller 4 and a follower roller 5.

[0010] A lever 6 acting as a carrier is hinged by means of a pin 7 and is always biased by the biasing force of a coil spring 8 toward the core 2, i.e., toward the outermost paper portion of the paper roll 1 (or in such a direction as is indicated by arrow A). As a result, the lever 6 can swing toward and away from the core 2, i.e., in the directions of arrows A and B in accordance with changes in the external diameter of the paper roll 1. The lever 6 thus constructed carries a slide plate 9 at its portion in which it comes close to the paper roll 1. More specifically, the slide plate 9 is carried or supported on the lever 6 by means of a guide shaft 10 anchored at the lever 6 such that it can slide in the longitudinal directions' of the lever 6, i.e., in the tangential directions of the paper roll 1 both forward (or in the direction of arrow C), in which the paper is to be let off from the paper roll, and backward (or in the direction of arrow D), in which the paper is to be taken up onto the paper roll 1. Here, the slide plate 9 is also biased in the direction D at all times by the biasing force of a backspin coil spring 11. At the same time, the slide plate 9 is biased roward the core through the guide shaft 10 and the lever 6 by the biasing force of the coil spring 8. As a result, the slide plate 9 is caused to apply a drag to the outermost paper portion of the paper roll 1 being fed. In order to ensure that drag, incidentally, a drag rubber 12 is placed to cover the surface of the slide plate 9, which is to be brought into contact with the outermost paper portion of the paper roll 1. Thus, the drag rubber 12 has a frictional face contacting with that outermost paper portion. The frictional face of the drag rubber 12 is shaped to extend generally flatly in the tangential directions of the paper roll 1 but to be bent at its trailing end away from the core 2 for smoothly contacting with the outermost paper portion of the paper roll 1.

[0011] The operations of the web feed mechanism thus constructed will be described in the following.

[0012] When the heat transfer carbon paper 1 is pulled, and unrolled in accordance with the progress of the printing operation at the thermal head 3, a frictional force is established between the drag rubber 12 and the carbon paper 1 so that the backspin coil spring 11 is compressed to have its biasing force strengthened by the pulling force through the frictional force established. In this meanwhile, the let-off portion of the carbon paper 1 is dragged and tensed until the slide plate 9 is brought in the forward direction C into a first position, as indicated by solid lines in Fig. 2, during one feed stroke of the carbon paper 1 against the biasing force of the coil spring 11 being strengthened.

[0013] Once the pulling force overcomes the biasing force of the coil spring 11 during that feed stroke, the let-off portion of the carbon paper 1 is pulled to frictionally slide on the surface of the drag rubber 12 so that the paper roll 1 is revolved to stepwise let off one pitch of the carbon paper 1 having a length corresponding to the turn of the platen roller 4. At this particular instant, i.e., just at the end of the feed stroke, the slide plate 9 still takes the first position shifted in the direction C while compressing the coil spring 11.

[0014] After that feed stroke, when the pulling force is weakened to zero so that it is overcome the biased- force of the coil spring 11, then the slide plate 9 is caused to frictionally or smoothly slide in the backward direction D on the outermost paper portion of the paper roll 1 into a second or initial position, as indicated by double-dotted lines in Fig. 2, by that biasing force thereby to pin back the paper roll 11. The weakening of the pulling force is also caused by the slackness of the let-off portion of the carbon paper 1 on the running path, as indicated by a double- totted line in Fig. 1, due to the overrun of the let-off paper portion, because the turn of the platen roller 4 is a stepwise or intermittent one so that it imparts an inertia at some level to the carbon paper 1. The slackness thus caused can be absorbed through the backward (i.e., in the direction D) frictional sliding movement of the slide plate 9 by the biasing force of the backspin coil spring 11. In other words, when the slide plate 9 is returned or brought in the backward direction D, the frictional force is restored between the drag rubber 12 and the carbon paper 1 to turn back the paper roll 1 in a direction, as indicated by letter E in Fig. 2, thereby to eliminate the slackness.

[0015] By repeating the stepwise operations thus far described, the slide plate 9 slides in the forward direction C and in the backward direction D to eliminate the slackness of the let-off carbon paper 1 on its running path thereby to prevent noises from being made. As is different from the simple dragging device of the feed mechanism of the prior art, moreover, the slip loss of the heat transfer carbon paper 1, which is caused at the thermal head 3 at the rise in the rotations of the platen roller 4, can be absorbed and dropped by the quick sliding movement of the slide plate 9 in the foward direction C. Still moreover, the carbon paper 1 on the running path can always be held under a constant tension by the drag which is ensured as a result of the frictional sliding movements of the slide plate 9 in the directions C and D and by the biasing force of the lever 6 in the direction A.

[0016] In the present embodiment, incidentally, the present invention has been described in case it is applied to the printer of stepwise feed type, but it can be applied to an arbitrary feed type. Moreover, the application of the present invention should not be limited to the heat transfer carbon paper having a very small thickness but to an arbitrary web.

[0017] In case the present invention is applied to the printer of continuous feed type, for example, the backspin coil spring 11 may bias the slide plate 9 in the backward direction D to hold the let-off portion of the carbon paper 1 under such a tension during the pulling operation as is caused by the balance between the drag and the pulling force.

[0018] As has been described hereinbeofre, according to the present invention, a very thin web such as the heat transfer carbon paper can be subjected to the back tension while being ensured to run forward and backward in the feed direction. As a result, no slackness occurs in the web on the running path so that the let-off portion of the web can be prevented from noises and/or undulating runs which might otherwise be casused by the fluctuations or interruptions of the tension applied thereto.

Claims

1. A web feed mechanism for feeding a web under a constant tension from a roll of web, comprising:

a carrier made movable toward and away from the center of the web roll and biased toward the same center;

a slide carried on said carrier in both manners to contact with the outermost web portion of said web roll and to slide in the tangential directions of said web roll both forward, in which said web is to be let off from said web roll, and backward, in which said web is to be taken up onto said web roll, for applying a drag to said outermost web portion; and

bias means for biasing said slide in said backward direction to hold the let-off portion of said web under such a predetermined tension during the web letting- off operation as is caused by the balance between said drag and a pullying force of the let-off portion of said web,

whereby the let-off portion of said web can be prevented from noises and/or undulating runs which might otherwise be caused by the fluctuations of the tension applied thereto.

2. A web feed mechanism according to Claim 1, wherein said carrier includes a lever hinged and biased toward the center of said web roll.

3. A web feed mechanism according to Claim 1, wherein said slide includes a drag rubber having a frictional face contacting with the outermost web portion of said web roll for ensuring said drag.

4. A web feed mechanism according to Claim 3, wherein said drag rubber has its frictional face extending generally flatly in said tangential directions but bent at its trailing end away from the center of said web roll for smoothly contacting with the outermost web portion of said web roll.

5. A web feed mechanism according to Claim 1, wherein said carrier includes a guide shaft mounted thereon for guiding the sliding movements of said slide.

6. A web feed mechanism according to Claim 5, wherein said bias means includes a backspin coil spring mounted around 3aid guide shaft and sandwiched under compression between said carrier and said slide.

7. A web feed mechanism for stepwise feeding a web, while tensing the same, from a roll of web, comprising;

a carrier made movable toward and away from the center of the web roll and biased toward the same center;

a slide carried on said carrier in both manners to contact with the outermost web portion of said web roll and to slide in the tangential directions of said web roll both forward, in which said web is to be let off from said web roll, and backward, in which said web is to be taken up onto said web roll, for applying a drag to said outermost web portion; and

bias means for biasing said slide in said backward direction, said bias means being adapted both to have its biasing force strengthened by a pulling force of the let-off portion of said web through a frictional force between said slide and said outermost web portion, while tensing the let-off portion of said web, until said slide is brought in said forward direction into a first position during one feed stroke of said web against the biasing force of said bias means being strengthened and to cause said slide to frictionally slide in said backward direction on the outermost web portion of said web roll into a second position by the strengthened biasing force which has overcome said pulling force after said one feed stroke, while spinning back said web roll, thereby to absorb a slackness, if any due to the overrun of the let-off portion of said web, through the backward sliding movement of said slide,

whereby the let-off portion of said web can be prevented from noises and/or undulating runs which might otherwise be caused by the interruptions of the tension applied thereto.

8. A web feed mechanism according to Claim 7, wherein said carrier includes a lever hinged and biased toward the center of said web roll.

9. A web feed mechanism according to Claim 7, wherein said slide includes a drag rubber having a frictional face contacting with the outermost web portion of said web roll for ensuring said drag.

10. A web feed mechanism according to Claim 9, wherein said drag rubber has its frictional face extending generally flatly in said tangential directions but bent at its trailing end away from the center of said web roll for smoothly contacting with the outermost web portion of said web roll.

11. A web feed mechanism according to Claim 7, wherein said carrier includes a guide shaft mounted thereon for guiding the sliding movements of said slide.

12. A web feed mechanism according to Claim 11, wherein said bias means includes a backspin coil spring mounted . around said guide shaft and sandwiched under compression between said carrier and said slide.

Drawing